This invention relates to a device for positioning and securing plate-shaped tools on a supporting and heating plate, intended for cutting of portions of metallic films and their hot-pressure transfer onto a paper or cardboard substrate, this device comprising means for securing said tools on said supporting and heating plate.
Relatively thick plates known as honeycomb plates in which are bored a plurality of evenly distributed rows of holes are already in use. These plates are adapted to receive a defined number of tools, constituting a type of printing plate, positioned and secured on the supporting plate. Such a supporting plate, thus provided with printing plates, is mounted in a machine that is fed with cardboard or paper blanks on the one hand and with metallic film webs on the other hand, for the cutting of metallic film portions and their hot transfer onto the cardboard blanks by the tools positioned on the supporting plate. Such mechanisms are, for example, used for printing onto packages. Usually the transfer or deposit of metallic films follows the operation of printing on the cardboard blanks. Thus, it is important that the printing plates be positioned accurately so that the transfer or deposit of the metallic films registers exactly with the imprints made by the printing operation.
One of the difficulties encountered in this process is that the transfer and the printing of these metallic film portions are performed in the hot state. Due to this fact, it is necessary to accurately adjust the position of the printing plates with respect to the operating temperature, taking into account the expansion of the supporting and heating plate from the ambient temperature to the operating temperature and the corresponding change of the respective positions of the printing plates on the supporting and heating plate.
Because of the cost of such a supporting and heating plate, in which the holes are highly accurate borings, it would be too expensive to use it to print only one packaging pattern. Consequently, only one supporting and heating plate is generally used for each machine. When changing the printing job it is, thus, necessary to remove the printing plates from the supporting plate and to position other printing plates corresponding to the next job. Since the printing plates operate in the hot state, this positioning must be performed on a plate having a temperature that corresponds to the operating temperature. Consequently, these requirements make the positioning operation difficult and exceedingly long. This operation typically takes a working day for each job change on a supporting and heating plate. Obviously, the cost of this operation impacts more heavily the cost of the printed workpieces in the case of relatively small printing jobs. Moreover, since the function of the supporting plate is not only to position the tools but also to heat them by contact, the use of a perforated plate substantially diminishes the contact surface at which the heating exchange takes place, and, thus reduces the efficiency of heating the tools.